The present invention relates to an optical pickup for optically reading an information signal recorded on a disklike recording medium.
Recently, portable use and personal use of compact disk players and data file apparatuses employing optical disks are gaining momentum and thus, optical pickups for use in these apparatuses are also required to be made smaller in size, especially in thickness. Thus, in response to recent demands for further reduction in size and thickness of such apparatuses, studies on reduction in size and thickness of optical pickups, an essential constituent element of the apparatuses, are widely conducted.
FIG. 1 schematically shows a known optical pickup for reading an information signal recorded on a disk 1 acting as an information recording medium. The known optical pickup includes a laser diode 2, a beam splitter 3, a mirror 4, an objective lens 5, a photodetector 6, an optical base 7 and an actuator 8 for actuating the objective lens 5. The optical base 7 has a boxlike shape and is made of synthetic resin or a metal. The laser diode 2, the beam splitter 3, the mirror 4 and the photodetector 6 are fixed to the optical base 7, while the objective lens 5 is incorporated in the actuator 8.
The known optical pickup of the above described arrangement is operated as follows. A portion of a beam emitted from the laser diode 2 is reflected by the beam splitter 3 and is deflected by the mirror 4. Thus, an optical spot having a diameter of about 1 .mu.m is formed on the disk 1 by the objective lens 5. Then, a beam reflected by the disk 1 takes reversely the route of the beam incident upon the disk 1 and is transmitted through the beam splitter 3 so as to be incident upon the photodetector 6. A light receiving face of the photodetector 6 is divided into a number of light receiving regions. By calculating signals detected by the respective light receiving regions, the information signal recorded on the disk 1, a focusing error signal corresponding to runout of the face of the disk 1 and a tracking error signal corresponding to eccentricity of recording tracks formed on the disk 1 are detected. On the basis of the focusing error signal and the tracking error signal, follow-up control of the objective lens 5 for runout of the face of the disk 1 and eccentricity of the recording tracks of the disk 1 is performed by the actuator 8 so as to actuate a focusing servomechanism and a tracking servomechanism.
However, in the above described arrangement of the known optical pickup, since the actuator 8 for driving the objective lens 5 in a tracking direction and a focusing direction is mounted on the optical base 7 to which the laser diode 2, the beam splitter 3, the mirror 4 and the photodetector 6 are secured, interior of the optical base 7 is exposed to atmosphere and thus, the laser diode 2 and the photodetector 6 are separately packaged so as to prevent moisture condensation and oxidation of the laser diode 2 and the photodetector 6. Therefore, the known optical pickup has such drawbacks that not only it is difficult to reduce size and thickness of the optical base 7 but optical characteristics of the known optical pickup deteriorate due to adherence of dust to or moisture condensation on a light transmission face of a package of each of the laser diode 2 and the photodetector 6 and surfaces of other optical elements.